Production of artificial filaments



Patented July 14, 1953 2,645,556 PRODUCTION OF ARTIFICIAL FILAMENTS Leslie Arthur Bashford and George Doubleday, Coventry, England, assignors to Courtaulds Limited, London, England, a British company No Drawing. Application June 4, 1952, Serial No. 291,804. In Great Britain July 25, 1951' Claims.

This invention relates to the production of artificial filaments and is particularly concerned with the production of polyacrylonitrile threads by wet spinning. The term polyacrylonitrile as used in this specification includes simple polymers of acrylonitrile and copolymers of a major proportion of acrylonitrile with a minor proportion of other polymerisable compounds such as styrene, methyl acrylate and vinyl acetate.

It has been proposed to produce polyacrylonitrile threads by wet spinning solutions of the polymer into coagulant baths; for example United States patent specifications Nos. 2,140,921 and 2,117,210 disclose that polyacrylonitrile solutions in aqueous solutions of hydrated salts can be reprecipitated by water, dilute salt solution and acids. It has also been proposed to wet spin polyacrylonitrile solutions in volatile organic solvents, such as dimethyl formamide, into coagulant baths composed of glycerol (United States patent specification No. 2,426,719), strong aqueous solutions of calcium chloride (United States patent specification No. 2,451,420) or aqueous solutions of zinc chloride, zinc bromide or zinc iodide (United States patent specification No. 2,467,- 553). Such baths are usually employed at high temperatures, for example of the order of 100 to 140 centigrade.

The object of the present invention is to provide an improved coagulant bath for polyacrylonitrile solutions suitable for use at ordinary temperatures.

According to the present invention, a process for the production of polyacrylonitrile threads includes the step of extruding a solution of polyacrylonitrile in .a water-miscible organic solvent into an aqueous coagulating bath containing potassium acetate in a concentration of from 20 per cent by weight up to saturation point. The coagulating bath is preferably used at ordinary temperatures that is from about to 25 centigrade but raised temperatures up to about 50 centrigrade may be used.

The polyacrylonitrile is preferably dissolved in dimethyl formamide but any other water-miscible solvent may be used. The concentration of the polymer in the solution is not critical and solutions containing from 15 per cent to per cent by weight of polyacrylonitrile have been spun satisfactorily into aqueous 55 per cent potassium acetate solutions.

The tensile properties of the threads obtained by the process of the present invention can be increased by subjecting the freshly formed threads either to a hot stretching process or to a cold stretching operation followed by a hot stretching process, for example in heated glycerol at 100 to 140 centigrade. The cold stretching step may be efiected in air at 15 to 40 centigrade by passing the thread over a series of rollers or godets which are designed to give the desired degree of stretch. The degree of cold stretch may vary between 20 per cent and 40 per cent. The hot stretching may also be efiected in known manner using rollers or godets. Such hot stretching is preferably at least 400 per cent and may be as high as 1000 per cent or more.

When it is desired to stretch the freshly-extruded filaments to produce high tenacity fibres, it is preferred to use nearly saturated potassium acetate coagulating baths, for example baths containing from about to per cent of potassium acetate; higher degrees of stretching can then be obtained together with an improvement in the general tenacity properties.

The process of the present invention is also particularly useful for the production of polyacrylonitrile staple fibres; In particular, the use of aqueous potassium acetate solutions as the coagulating bath permits the use of jets having a large number of holes; for example jets having 500, 1000, 2500 and 3750 holes may be used. The filaments issuing from such jets can be collected into a tow of substantially parallel filaments, processed in tow form, cut and dried.

By applying a high degree of stretch as described above, for example using a combination of cold and hot stretching, high strength staple fibres of deniers as low as 1.5 can readily be produced. The stretching of tows is preferably effected by using a series of take-up devices each consisting of two take-up reels with their axes inclined. The reels preferably have a discontinuous surface made up of a number of interdigitating bars mounted on reel members as in normal reel construction, but instead of the axes of the reel members being offset and askew, they are concentric. By the use of such reels, the incidence of broken filaments and the lapping of such filaments round the take-up device is minimised.

The present invention is illustrated by the following examples in which parts and percentages are by weight:

Example 1 A polyacrylonitrile prepared by p-olymerising acrylonitrile in aqueous solution with ammonium persulphate as catalyst and having an intrinsic viscosity of 1.42, was dissolved in dimethyl form- The skein was washed withwater till it was free from potassium acetateaandz: glycerol and then dried, free from tension, in an air. current at 65 centigrade.

The thread obtained was pale cream in colour The thread was then.

and had a warm handle, while the individual I filaments were separate and possessed a pronounced crimp.

Tests on the individual filamentsgavethe following results: i

Denier 3.0-1; Tenacity (dry) Not less than 3.3 grams perdenier. Extensibility; Not less than 32 per' cent Example 2 The procedure described in Example 1 was repeatedwith the following variations only:

(a) The spinning solution was a per cent solution in dimethyl formamide ofa polyacrylonitrile having an intrinsic viscosity of 1.10.

(b) The initialtak'ei-up .speedwas 7 metres per minute. I

(c) The stretching was 1291per centin glycerol at 142 centigrade.

Tests on individual filaments gave the following results:

Denier; 2.52.

Tenacity 3 .12- grams per denier.

Extensibility--- 38.1 per cent.

Example 3 Q A polyacrylonitrile. prepared by polymerising acrylonitrile in aqueous solution with ammonium persulphate as catalystand having an intrinsic viscosity of 1.08 was dissolved in dimethyl formamideto form a 17 per cent solution. The solution, after filtration and de-aeration,. was ex-' tru'ded. through a multi hole jet into acoagulating bath at 23 centigrade consisting, of a neutral concentrated aqueous potassium acetate solu' tion, specific gravity 1.32 at 25 centigrade: The length of immersion was 20 inches and the thread was then passed on to a seriesof'thread advancing'rollers designed to stretch the thread 33 percent in air at 23 centigrade. The thread was then stretched a further 1079 per cent while passing through a bath of glycerol at about 135 centigrade and the stretched thread was collected on a skein reel at a'rate of 83 metres per minute. The skein was washed with water till it was free from potassium acetate and glycerol and then dried, free from tension, in an air current at 60 Centigrade.

Tests on the individual filaments gave the following mean results:

Denier 3.42. Tenacity 5.62 grams per. denier. Extensibility 21.3 per cent.

Example 4 A polyacrylonitrile prepared by polymerising acrylonitrile in aqueous solution with ammonium persulphate as catalyst and having an intrinsic viscosity of 1.10 to 1.15, was dissolved in dimethyl formamide to form a 16 per cent solution. The solution, after filtration and cle-aeration, was extruded through a jet having 500', 2.5 mil holes into a coagulating bath at 23 Centigrade consisting of a neutral concentrated aqueous potassium acetate: solution, specific gravity 1.32 at 25 Centigrade. The length of immersion was 21 inches and the filaments were collected into tow formand passed on to a pair of rotating threadadvancing rollers having a peripheral speed of 5.04 metres per. minute and then to a second andthird'pairof rollers both with a peripheral speed. of 6.72 metres per minute thereby giving a cold stretch of 33 per cent. The tow was then stretched a further 1105 per cent (giving 1520 per cent total-stretch) while passing through a bath of glycerol at to centigrade and the stretched tow was passed to a pair of inclined reels arranged-to form a tow collecting and advancing device. The tow was then passed to a cutter where the filaments were cutinto 1% inches stap'lelength andthe cut fibres were washed with water till free from potassium acetate and glycerol and then dried.

Ihe individual fibres-possessed a pronounced crimp, and tests on thefibres-gave the following mean results:

Denier 1.44.

Tenacity (dry) 5.89grams per denier.

Extensibility 30.6. per cent.

Example 5 A 16 per cent solution of polyacrylonitrile in dimethyl formamide as used in Example 1, after filtration and de-aeration, was extruded through a jet having 2500.holes,.each 2 mils indiameter, into an aqueous 58 per cent potassium acetate solution at 25 Centigrade. The filament immersion was 20 inches and the tow of filaments'was passed on' withdrawal from the bath to a pair of rotating thread-advancing rollers having a peripheral speed of 5.7 metres per minute and then to a second pair of rollers having' a peripheral speed of 7.7 metres per minute giving a 35 per cent air stretch. The tow was then stretched in glycerol at centigrade to a speed of 56.0 metres per minute, giving a total stretch of 880 per cent. The tow was then cut to staple length, washed-and dried as described in Example 4.

The individual fibres had a pronounced crimp and tests on the fibres gave the following mean results:

Denier 2.33.

Tenacity 3.81 grams per denier.

Extensibility 42.6 per cent.

Eram'ple 6 A 16 per cent solution ofrpolyacrylonitrile in dimethyl formamide as used in Example 4, after filtration and deaeration, was extruded through a jet having 503.0 mil holes into a- 30 per cent aqueous potassium acetate solution at 25 centigrade. The lengthof immersion was 21 inches and the filaments were collectedinto tow' form and passed on to a pair of rotating thread-advancing rollers having aperipheral speed of 10.5 metres per minute. and then to a second and third pair of rollers both with a peripheral speed of 14 metres per minute thereby giving a cold 33 /3 per cent stretch. The tow was then further stretched in glycerol at 135 centigrade to a speed of 69 metres per minute giving a total stretch of 5'76 per cent. The filaments were collected on a skein reel, washed with water till free from glycerol and potassium acetate and then dried.

Fibre properties were as follows:

Denier 1.6. Tenacity 3.66 grams per denier. I Extensibility 23.1 per cent.

Example 7 Example 6 was repeated with the following variations only:

(a) The coagulating bath was a 40 per cent aqueous potassium acetate solution and (b) The final speed was 73.5 metres per minute giving a total stretch of 600 per cent.

Fibre properties were as follows:

Denier 1.44.

Tenacity 3.94 grams per denier.

Extensibility 18.3 per cent.

Example 8 Denier 1.40. Tenacity 4.11 grams per denier. Extensibility 29.9 per cent.

What we claim is:

1. A process for the production of polyacrylonitrile threads which includes the step of extruding a solution of polyacrylonitrile in dimethyl Number formamide into an aqueous coagulating bath containing potassium acetate in a concentration of from 20 per cent by weight up to saturation point.

A process for the production of polyacrylonitrile threads which includes the step of extruding a solution of polyacrylonitrile in dimethyl formamide into an aqueous coagulating bath, said bath being at a temperature of from about 15 centigrade to about 25 centigrate and containing potassium acetate in a concentration of from 20 per cent by weight up to saturation point.

3. A process for the production of polyacrylonitrile threads which includes the step of extruding a solution of polyacrylonitrile in dimethyl formamide into an aqueous coagulating bath containing potassium acetate in a concentration of from about to per cent by weight.

4. A process for the production of polyacrylonitrile staple fibres comprising the steps of extruding a solution of polyacrylonitrile in dimethyl formamide through a jet having at least 500 holes into an aqueous coagulating bath containing p0- tassium acetate in a concentration of from 20 per cent by weight up to saturation point, collecting the filaments issuing from the jet into a tow of substantially parallel filaments, processing the tow, cutting the tow into staple lengths and drying the cut fibres.

5. A process as claimed in claim 4 wherein the tow of parallel filaments is stretched from 20 to 40 per cent in air at 15 to 40 centigrade and is subsequently further stretched in glycerol at to centigrade.

LESLIE ARTHUR BASHFORD. GEORGE DOUBLEDAY.

References Cited in the file of this patent UNITED STATES PATENTS Name Date Hare Apr. 19, 1949 Hochwalt Mar. 6, 1951 l-Ioxie Dec. 11, 1951 

1. A PROCESS FOR THE PRODUCTION OF POLYACRYLONITRILE THREADS WHICH INCLUDES THE STEP OF EXTRUDING A SOLUTION OF POLYACRYLONITRILE IN DIMETHYL FORMAMIDE INTO AN AQUEOUS COAGULATING BATH CONTAINING POTASSIUM ACETATE IN A CONCENTRATION OF FROM 20 PER CENT BY WEIGHT UP TO SATURATION POINT. 